/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.expression.common;

import org.springframework.core.convert.TypeDescriptor;
import org.springframework.expression.EvaluationContext;
import org.springframework.expression.EvaluationException;
import org.springframework.expression.Expression;
import org.springframework.expression.TypedValue;
import org.springframework.lang.Nullable;

/**
 * A very simple hardcoded implementation of the Expression interface that represents a
 * string literal. It is used with CompositeStringExpression when representing a template
 * expression which is made up of pieces - some being real expressions to be handled by
 * an EL implementation like SpEL, and some being just textual elements.
 *
 * @author Andy Clement
 * @author Juergen Hoeller
 * @since 3.0
 */
public class LiteralExpression implements Expression {

    /**
     * Fixed literal value of this expression
     */
    private final String literalValue;


    public LiteralExpression(String literalValue) {
        this.literalValue = literalValue;
    }


    @Override
    public final String getExpressionString() {
        return this.literalValue;
    }

    @Override
    public Class<?> getValueType(EvaluationContext context) {
        return String.class;
    }

    @Override
    public String getValue() {
        return this.literalValue;
    }

    @Override
    @Nullable
    public <T> T getValue(@Nullable Class<T> expectedResultType) throws EvaluationException {
        Object value = getValue();
        return ExpressionUtils.convertTypedValue(null, new TypedValue(value), expectedResultType);
    }

    @Override
    public String getValue(Object rootObject) {
        return this.literalValue;
    }

    @Override
    @Nullable
    public <T> T getValue(Object rootObject, @Nullable Class<T> desiredResultType) throws EvaluationException {
        Object value = getValue(rootObject);
        return ExpressionUtils.convertTypedValue(null, new TypedValue(value), desiredResultType);
    }

    @Override
    public String getValue(EvaluationContext context) {
        return this.literalValue;
    }

    @Override
    @Nullable
    public <T> T getValue(EvaluationContext context, @Nullable Class<T> expectedResultType)
            throws EvaluationException {

        Object value = getValue(context);
        return ExpressionUtils.convertTypedValue(context, new TypedValue(value), expectedResultType);
    }

    @Override
    public String getValue(EvaluationContext context, Object rootObject) throws EvaluationException {
        return this.literalValue;
    }

    @Override
    @Nullable
    public <T> T getValue(EvaluationContext context, Object rootObject, @Nullable Class<T> desiredResultType)
            throws EvaluationException {

        Object value = getValue(context, rootObject);
        return ExpressionUtils.convertTypedValue(context, new TypedValue(value), desiredResultType);
    }

    @Override
    public Class<?> getValueType() {
        return String.class;
    }

    @Override
    public Class<?> getValueType(Object rootObject) throws EvaluationException {
        return String.class;
    }

    @Override
    public Class<?> getValueType(EvaluationContext context, Object rootObject) throws EvaluationException {
        return String.class;
    }

    @Override
    public TypeDescriptor getValueTypeDescriptor() {
        return TypeDescriptor.valueOf(String.class);
    }

    @Override
    public TypeDescriptor getValueTypeDescriptor(Object rootObject) throws EvaluationException {
        return TypeDescriptor.valueOf(String.class);
    }

    @Override
    public TypeDescriptor getValueTypeDescriptor(EvaluationContext context) {
        return TypeDescriptor.valueOf(String.class);
    }

    @Override
    public TypeDescriptor getValueTypeDescriptor(EvaluationContext context, Object rootObject)
            throws EvaluationException {
        return TypeDescriptor.valueOf(String.class);
    }

    @Override
    public boolean isWritable(Object rootObject) throws EvaluationException {
        return false;
    }

    @Override
    public boolean isWritable(EvaluationContext context) {
        return false;
    }

    @Override
    public boolean isWritable(EvaluationContext context, Object rootObject) throws EvaluationException {
        return false;
    }

    @Override
    public void setValue(Object rootObject, @Nullable Object value) throws EvaluationException {
        throw new EvaluationException(this.literalValue, "Cannot call setValue() on a LiteralExpression");
    }

    @Override
    public void setValue(EvaluationContext context, @Nullable Object value) throws EvaluationException {
        throw new EvaluationException(this.literalValue, "Cannot call setValue() on a LiteralExpression");
    }

    @Override
    public void setValue(EvaluationContext context, Object rootObject, @Nullable Object value)
            throws EvaluationException {
        throw new EvaluationException(this.literalValue, "Cannot call setValue() on a LiteralExpression");
    }

}
